My answer: If we take any two sequences of real numbers a_n and b_n that tend to zero as n to infinity, then we have that (a_n, b_n) -> (0,0) and f(a_n, b_n) = sin(a_n b_n)/a_n and since for small values of x, sin(x) is very close to x we have that f(a_n, b_n) has the same limit as a_n b_n / a_n = b_n which goes to 0 = f(0,0). Thus it is continuous at (0,0).